Though West Nile virus has recently been watched for its impact on dogs, to date only a handful of dogs with the virus have died — though the virus was not necessarily the cause of death. A vaccine has been produced for horses, a species that is acutely affected by the virus. However, no vaccine has been developed for canines; at this time, there is not a need for one.

Researchers continue to keep an eye on this virus and many others. Viruses frequently mutate to survive. Parvovirus is one such example. The vaccine for this virus has undergone several modifications to account for these changes and to make sure that the antibodies produced by the dog could fight off the newest version of the disease.

Additionally though uncommon, viruses do cross species. In 2004, for example, an equine virus mutated and infected a large population of racing greyhounds in Florida. The virus was contained, but it is easy to see how a disease can unexpectedly jump from one species to another.

In addition to altered viruses, the danger of foreign diseases traveling from countries around the world and infecting dogs in the United States is quite possible. With the speed of air travel, it is feasible for an infected host to survive the flight and potentially find a new host here. It's certainly not something to lose sleep over; however, it's good to be aware that diseases are not static and that they will mutate, travel, or cross species to improve their chances of surviving.